Between 1979 and 1986 he built high-tensile fences for a living, an experience he drew upon for his first novel, The Restraint of Beasts. In 1986 Mills moved to London and became a bus driver, used for his 2009 novel The Maintenance of Headway. Although much was made in the British press of Mills' bus-driving background, in reality he had written a column for The Independent before becoming a novelist.[1] (Rumours also claimed that he'd earned a total of £1 million, but the real figure was closer to £10,000.[2]) Mills later claimed that he lost his gig at The Independent when "one week, in exactly the same place that my column had been, there was a new item entitled 'Bridget Jones' Diary'."[3]

His 2005 novel, Explorers of the New Century, was released to good reviews from The Sunday Times,[4]The Independent,[4] and The Telegraph,[5] among others. Having written his first quartet of novels for Flamingo, Explorers of the New Century marked a new partnership with Harry Potter publishers Bloomsbury. Mills' has also written two books of very short stories, Once in a Blue Moon and Only When the Sun Shines Brightly for Acorn Books. In his 2011 novel A Cruel Bird Came to the Nest and Looked In, Mills depicts a kingdom whose king has gone missing without explanation, leaving an absurdist realm "lost in an English fairy-tale world."[6]

Magnus Mills' style has been called 'deceptively' simple.[7] His prose style is rhythmic, often repetitious, and his humour is deadpan. He favours short sentences, little description and a lot of dialogue. Mills has cited Primo Levi as a key influence.[8]

Magnus Mills' books usually feature one or more working-class men as the protagonist(s).[9] In The Restraint of Beasts, an unnamed supervisor works alongside two Scottish fence-builders as they move from location to location building high-tensile steel fences. The theme of repetition is established early on, as the men fall into a routine of working during the day, going to the local pub at night and 'accidentally' killing people along the way. The same kind of skewed repetition occurs in Mills' later works All Quiet on the Orient Express and The Scheme for Full Employment. All Quiet on the Orient Express is about a man who stops at a camp site in the Lake District to kill some time before embarking on a journey on the Orient Express. Gradually, he becomes involved in the local community and offered jobs until it becomes clear that he may never leave. The Scheme for Full Employment tells of a "beautiful" scheme whereby people are employed to drive around on set routes, stopping at depots to offload the contents of their vans.

Freedom is a key theme in Mills' work.[10] What do the fences in The Restraint of Beasts suggest? Who, or what are the 'beasts'? Can the protagonist of All Quiet on the Orient Express ever assert his freedom? Does it exist? This theme is explored most vividly in Three to See the King, whose characters live in a largely allegorical world that lacks many of the identifiable conventions of working class life—they don't have jobs, pubs or anything more than a rudimentary social network. The main character attempts to establish a simple freedom for himself within his small, beloved house, only to find himself at the mercy of unsolicited relationships and the ideology of a charismatic newcomer. Like most of Mills' characters, he remains desperately attached to his routine, attempting to meet each twist with a calm, reasonable approach, until it becomes impossible. In Explorers of the New Century, the characters begin as masters of their mules and the art of exploration, but as their journey continues, the harsh climate and terrain of the land strip them of control over their own destinies. At the outset of the book, the explorers are able to assign or deny freedom to their mules; by the end, most of the explorers are dependent on the mules for their own freedom.

Mills himself has talked about themes of punishment and reward as being key themes in his work, particularly in The Restraint of Beasts.[11] The leaders of the expeditionary teams in Explorers of the New Century struggle with punishment as a means of encouraging and disciplining their mules, never able to achieve exactly the results they desire but fearful of interacting with the mules by any means more complex than punishment and reward.